Layers of Mystery
From any angle, the 2.15-carat blunt-end, bullet-shaped stone offers a range of colors that is unique in the diamond world. It is at once fancy deep orange-brown at one end, merging into fancy dark gray-yellowish green at the other. Even more intriguing, the remarkable chameleon quality of the diamond is confined to the gray-yellowish green zone of the stone. That’s a lot of variety within one small, modified rectangular diamond.
While the fancy deep orange-brown portion of the stone is completely stable, when the stone is heated, the chameleon portion gradually changes into a clean yellow color within a few minutes. As it cools back to room temperature, the original color — the gray-yellowish green — returns. In addition, the green end of the diamond — the unstable chameleon color — also reverts to yellow when it is contained in a dark environment, such as a vault.
According to the Gemological Institute of America’s (GIA) monograph on this stone, “Scientists do not yet fully understand the mechanism that causes this color-change behavior in diamond but presumably it is the result of an input of energy, in the form of heat or light, creating a temporary ‘color center’ defect in the diamond lattice. This temporary defect no longer exists when the source of energy is removed, and the unstable color changes back to the stable color.”
Cutting Challenges
The cutter who worked on this rough already was dealing with significant inclusions. Whatever initial plan he had to enhance the bicolor nature of the stone may also have had to be amended to make the most of the color-change part of the stone. Cutting the stone with long parallel facets was a natural choice for a bicolor stone; it allows the eye to observe and enjoy the color transitions. The step-cut shape of the stone makes the most of the rough, allowing the range of colors of the diamond to be well displayed.
This unique bicolor chameleon diamond has been exhibited widely over the past two years, including a stint at the American Museum of Natural History in New York City. Sacheti intends to find a permanent home for the stone in some museum. It is simply too special, he feels, not to be shared.
